The Gut Brain Connection
The human gut contains microbes that play a critical role in digestion, metabolism, and immune function. This gut microbiome communicates with the brain and vice versa, creating the gut brain connection.
Meet Dr. Emeran Mayer
Dr. Emeran Mayer, a Distinguished Research Professor in the Departments of Medicine, Physiology and Psychiatry at the David Geffen School of Medicine at UCLA (DGSOM), is an internationally renowned pioneer in research on the gut brain connection.
He is director of the UCLA Brain Gut Microbiome Center, executive director of the G. Oppenheimer Center for Neurobiology of Stress and Resilience and author of The Mind-Gut Connection.
Growing up in Bavaria, his family ran a confectionary business. He recalls different sweet, tempting aromas filling the building, especially during the holidays.
“The products we made were really about positive social interactions: weddings, birthdays, big holidays,” he says. “So I’ve always associated delicious food with social interactions, and now my research touches on this hedonic aspect of food intake. I’m sure my childhood experiences planted the seed of my interest in that area.”
During his medical training, he became fascinated with the idea that the brain exerts a major influence on organs.
“None of the physicians or researchers thought the brain played any role in gut diseases,” he says, laughing as he recalls the resistance he met when he first began investigating the gut brain connection.
“And now it has become such a trendy topic. Everyone wants to know how to improve gut health.”
(What Is a Gastroenterologist? Click the link to learn more...)
What Is IBS?
What Is Irritable Bowel Syndrome?
Irritable Bowel Syndrome (IBS) is, as defined on the UCLA G. Oppenheimer Center for Neurobiology of Stress and Resilience website:
A chronic or recurrent gastrointestinal condition characterized by abdominal pain, discomfort and altered bowel habits, i.e., diarrhea and/or constipation. It is considered a “functional” bowel disorder which refers to the fact that these conditions cannot (yet) be reliably diagnosed by blood tests, abdominal imaging studies, tissue samples, or other routine tests; that is, they cannot be easily explained by anatomic or structural abnormalities.
IBS-C vs. IBS-D
IBS-C and IBS-D are both different subtypes of IBS. The types are determined based on the patient’s most prominent bowel habits.
- IBS-C (IBS Constipation) is characterized by constipation.
- IBS-D (IBS Diarrhea) is characterized by diarrhea.
What Causes IBS?
Many different intertwined factors likely cause IBS to develop. Studies suggest the following potential IBS causes:
- Genetics, as IBS runs in families
- Chronic stress, especially early-life stress
- Intestinal infections
No single factor has been isolated as a direct cause of IBS. However, experts agree that it develops after a brain gut communication disturbance impacts bowel function.
“IBS is regulated at the brain level and also at the gut level—through the little brain inside the gut—at the same time,” says Dr. Mayer.
“I prefer not to call it the gut brain axis like some people do, because that implies a linear system. It’s actually a loop; it’s bi-directional. No matter where the problem starts, it always feeds back and involves the other components as well.”
The little brain inside the gut is the enteric nervous system, which regulates the gut-based immune system, endocrine system, glial cells and epithelial cells.
Gut Health and Anxiety
A relationship between anxiety and gut health exists because of the bi-directional nature of communication between the brain and the gut. Anxiety may cause an IBS flare up. Conversely, IBS flare ups may cause psychological shifts.
“We know from large-scale genetic studies that IBS and anxiety disorders share the same risk genes,” Dr. Mayer says. “And IBS patients usually have higher than average anxiety ratings.”
The most frequently referenced IBS symptoms include:
- Abdominal/stomach pain
- Abdominal swelling
- Mucus in the stool
- Urgent bowel movements
- Bowel leakage
- Lack of relief following bowel movements
Symptoms of IBS in Women Vs. Men
IBS may create different symptoms in women and men due to a combination of hormonal, physiological, psychological, and psycho-social factors.
Dr. Mayer and his team were among the first to use functional magnetic resonance imaging (MRI) and positron emission tomography (PET) scanning to investigate how brain activity differs among IBS patients of different sexes.
Combining the results of those studies with observational research, they identified:
Biologically determined sex differences that are detectable using brain imaging or by studying the microbiome or hormone levels.
For example, female IBS patients may experience elevated symptoms at the menstrual-cycle onset, which suggests a possible relationship between reproductive hormones and IBS symptoms.
Psychologically and psycho-socially influenced sex differences.
These factors often impact an individual’s likelihood of visiting a gastroenterologist to seek diagnosis and care.
“Women are about four times as likely as men to see a gastroenterologist,” says Dr. Mayer. “So really, both men and women may have the same symptoms, but women react to them differently.”
Some sex disparities in IBS symptoms may be rooted in the different ways men and women process pain in the brain’s salience system, which evaluates the perceived threat of any homeostatic change.
- In men, there's typically more activation in the insular cortex, which governs sensory processing.
- In females, there’s typically more activation in the amygdala and other areas of the emotional arousal circuit.
Do I Have IBS?
People can find out if they have IBS by visiting a gastroenterologist to be evaluated.
How Is IBS Diagnosed?
Practitioners diagnose IBS based on symptoms. One universal symptom is abdominal pain that occurs for at least three days out of a month and that is associated with diarrhea and/or constipation.
Physicians will likely run more in-depth tests on patients with additional symptoms, including bloody stools or unintentional weight loss, to rule out other diseases, such as colon cancer, celiac disease, and inflammatory bowel disease.
Irritable bowel syndrome self-care is a core facet of treatment. It requires patients to observe and determine:
- What particular IBS symptoms they have
- What factors (food, environment, stress) increase or mitigate their particular symptoms
This approach works best because IBS symptoms vary from patient to patient. No single IBS treatment will work for all patients.
Practitioners may also recommend additional treatments and irritable bowel syndrome medications, including:
- Herbal medications, fiber supplements, probiotics, and laxatives for IBS constipation
- Antidiarrheal medications, antibiotics, and the serotonin medication alosetron for IBS diarrhea
- Behavioral techniques, including meditation, stress management, cognitive behavioral therapy, relaxed breathing techniques, or hypnosis
Irritable Bowel Syndrome Diet
IBS patients should be mindful of their diets. The following foods may aggravate symptoms, including IBS bloating and IBS pain, in some patients:
- Milk products in lactose-intolerant patients
- Dietary fats
- Fruits with high fructose levels, such as apples and grapes
- Vegetables that cause gas, such as broccoli and cabbage
- Artificial sweeteners such as sorbitol
IBS Awareness Month
For IBS Awareness Month, Dr. Mayer wants to clarify a few common misconceptions about IBS:
While IBS does involve a spastic colon, it’s not only a disease of a spastic colon.
“It's much more elaborate and involves the microbiome system, which is complex and has multiple components.”
No diet is an IBS cure.
“Many people believe there’s a miraculous diet that can resolve all symptoms, when really, it’s much more individual. People need to figure out which diet works best for them.”
IBS is a gut disease, but it also has a lot to do with the brain.
“A lot of patients may be resistant to the idea that what’s happening in their gut is deeply connected to what’s happening in their brain.”
Misconceptions aside, Dr. Mayer marvels at how far the understanding and acceptance of IBS and the gut brain connection has come since he first started investigating it.
“People originally thought IBS didn’t really exist or was just gas,” he says. “It’s definitely a disorder of brain gut interactions. Numerous factors, including mental state, psychological stress, and diet, play major roles in modifying the severity of symptoms. If you want to treat it effectively, you should address all these dimensions in a multidisciplinary approach.”